Although metal corrosion in wastewater plants has been looked at for a long time, the importance of corrosion on concrete or mortars has attracted attention only in recent years. Corrosion damage, in particular corrosion damage caused by microbial metabolism of sulfur compounds, are among the more frequently occurring types of damage in wastewater conduits; in addition, there is damage to pumping stations and in wastewater purification plants (treatment plants). The corrosive destruction of concrete or mortar surfaces due to biologically generated (biogenic) sulfuric acid is also observed in biogas plants. The sulfuric acid is formed as metabolite by bacteria of the Thiobacillus type living in the aerobic region of wastewater plants or biogas plants. Cement-based materials and lime-containing aggregates are attacked (dissolving and swelling attack) by the sulfuric acid. The effects are considerable: the corrosion rate is, depending on conditions, reported as 6-10 mm/year. The result is a typical washed concrete surface of the damaged concrete (exposure of the rock particles).
It is known from the prior art that the acid resistance of concrete can be improved by combining cements with pozzolanic additives: JP 2002160960 A2 describes a hydraulically setting composition comprising high-alumina cement with pozzolanic additives such as fly ash. Compositions comprising cement and a fine pozzolanic powder are described in JP 2003055019 A2. JP 2006327868 A2 describes compositions comprising high-alumina cement, slag sand and a shrinkage-reducing additive. JP 2006-225221 A2 relates to mortar compositions comprising calcium aluminate cement, pozzolanas and iron-free slag sand, optionally mixed with polymer dispersions or fibers. JP 2006/044958 A2 describes an acid-resistant mortar comprising high-alumina cement, slag sand, polymer dispersion and shrinkage-reducing additive. A mortar composition comprising portland cement, slag sand, a further inorganic binder, acrylate or styrene-butadiene polymer is known from KR 20040089995 A. EP 1614670 A2 relates to cement-based mortar systems based on portland cement clinker, calcium aluminate cement and additives from the group of pozzolanas and latent hydraulic materials. A similar composition comprising portland cement, pozzolana, latent hydraulic binder such as slag sand, with polymer dispersion, water-soluble polymer or expanded clay being able to be added, is described by JP 2007001802 A2.
Although these systems display rapid setting behavior due to the presence of cement, the acid resistance is not satisfactory.